FIG. 1 illustrates a conventional process 100 for preparing a photoresist. In process 100 a photoresist is provided on a substrate to form a coating in block 12, and then the photoresist coating is soft baked via block 14. Exposure of the coating through a mask is then performed via block 16. Process 100 proceeds to bake the resist coating after exposure via block 18, a procedure known as post exposure bake. A post exposure bake procedure is considered necessary to forman image in the resist. The conventional process concludes with development block 19, in which the pattern on the mask is transferred to the resist coating.
Features patterned with photoresist masks prepared in accordance with process 100 have demonstrated deformed sidewalls in certain photolithography processes. FIG. 2A depicts a photoresist 30 on substrate 32. Photoresist 30 has been baked after exposure in accordance with the method of FIG. 1. As a result of performing a post exposure bake, the top and bottom resist critical dimension (CD) shrink to form the curved side walls 35 of FIG. 2A. After development, sidewall 35 of photoresist 30 has a deformed profile that deviates from the substantially vertical sidewalls that are desirable for fabricating microelectronic structures. Thus, process 100 generates photoresists that are unsuitable for forming microelectronic structures with predetermined critical dimensions.
A photoresist processed in accordance with the method of FIG. 1 was used to define the side shields 20 of FIG. 2B. On substrate 22, side shields 20 are shown flanking cavity 25 in an intermediate structure. Intermediate structure may be used to fabricate, for example, a magnetic recording head. Cavity 25 has a narrower opening f near top 23, and a much wider opening g near base 28. Specifically, FIG. 2B illustrates an intermediate structure having a width f near the top 23 of cavity 25 and a width g near base 28 of cavity 25. Since width f is significantly dissimilar to width g, the sidewall profile of features patterned with photoresists prepared by process 100 adversely impacts the critical dimensions of patterned devices.
It is believed that post exposure baking can deform photoresist sidewalls prepared in accordance with process 100. Therefore, photoresists prepared in accordance with process 100 impartan undesirable curvature to side shields 20 in FIG. 2B.
In light of the aforementioned problems, there is a need for improving the methods for processing photoresists for high resolution lithography.